Key outcomes

  • Mitigated risk
  • Reduced emissions and operating costs
  • Provided never-before-seen understanding of the internal behaviour 

The multiple hearth furnace, or MHF, is a design used for many applications worldwide, including calcination, carbon activation/regeneration and biosolids incineration.

Synergetics' CFD modelling accounted for both the drying and devolatilisation processes, as well as the combustion, to accurately predict the temperature of combustion by-products.

Hot gasses and cake particles in an MHF

Figure 1: Hot combustion gasses created by hearth two combustion.

Performing CFD simulations of a MHF was a novel, untested approach, so validating the model was critical to presenting the client with reliable predictions. This validation was performed using an onsite data measurement campaign, which coupled temperature and gas sensor readings at the furnace exit and stack, together with lab tests on feed composition to provide accurate inputs for the model, and outputs to validate against.  A target difference of 20% on hearth temperatures, and exit gas O2, CO and CO2 levels was set in order for the model to be considered valid. The validation was performed under two sets of operating conditions, and strong agreement was observed, with all validated quantities well under the 20% criteria.

The next stage was to use the model to predict the impact of predicted future operational loads on the furnace, and identify potential future issues.  Using the model, design and operation recommendations were provided which would reduce emissions and operating costs. Additionally a wide range of proposed engineering changes were simulated and assessed, allowing the optimal solution to be determined, mitigating the client’s risk of undertaking costly capital changes without achieving the desired improvements in stability and emissions.

 

Figure 2: An animation showing the motion of cake as it is raked by the rabble arms.